The present invention relates to a semi-automated or automated transmission system for a vehicle with a manual over-ride means such as a manual control input. Transmission systems of the kind that the invention relates to have a clutch, such as a main drive clutch, clutch-actuator means for controlling the state of engagement of the clutch, a multi-speed transmission, a gear-engaging mechanism for engaging an operative ratio of the transmission, and a driver-operable gear-selector lever allowing a driver to select the operative ratio.
With transmission systems of this type, when starting the vehicle from standstill, the clutch is taken out of engagement and a start-up gear is selected automatically. The clutch is then brought into engagement, while at the same time the throttle of the vehicle is being actuated. A transmission system of this type is disclosed in UK Patent No. 2302377. The content of said UK patent is hereby expressly incorporated by reference in the disclosure of the present application.
Conventionally, when the transmission system is put into drive, the first gear is automatically selected as the start-up gear. This is appropriate under normal road conditions. However, when traction on the road surface is reduced due, for example, to snow or ice, it may be desirable to select a higher gear ratio, for example second or even third gear, in order to reduce the torque applied to the driven wheels of the vehicle when starting up from a standstill condition.
The object of the present invention is to improve a state-of-the-art transmission system of the type described above, so as to increase the level of comfort and safety of a vehicle that is equipped with a transmission system according to the invention.
The present invention meets the foregoing objective for a vehicle transmission system that includes a main drive clutch, clutch-actuator means for controlling the degree of engagement of the clutch, a transmission with a plurality of gear ratios, a gear-engaging mechanism for engaging an operative ratio of the transmission, a driver-operable gear-selector lever allowing the driver to select the operative ratio, and an electronic control means to control the clutch-actuator means and gear-engaging mechanism. The control means, which includes means for initiating a start-up from a standstill condition of the vehicle, is designed to disengage the clutch and to automatically shift into a start-up gear when the start-up phase of the vehicle is initiated from a standstill condition. According to the invention, if the driver selects a higher start-up gear by operating the gear-selector lever while the vehicle is at rest and the automatically selected start-up gear is engaged, the control means is designed to engage said higher start-up gear.
In accordance with the present invention, the driver may influence the selection of the start-up gear, e.g., in a case where the road conditions require a higher start-up gear than the one that is automatically engaged.
In accordance with one embodiment of the invention, the control means will automatically shift the transmission into first gear upon initiation of the start-up phase out of a standstill condition. The gear level may be increased to second or even third gear by appropriate movement of the gear-selector lever at a time when the vehicle is at rest with the automatically selected first gear engaged and before the throttle is actuated to set the vehicle in motion.
After increasing the start-up gear in this manner, the higher gear would be retained as the lowest ratio available, until deselected as described below. While the vehicle is in motion with a higher start-up gear imposed, gear levels equal and higher than the increased start-up gear may be engaged either manually or automatically. Changes to a lower gear level than the increased start-up gear would, however, be inhibited.
The higher start-up gear may be deselected by:
a) moving the gear-selector lever to select a lower gear while the vehicle is at rest with the higher start-up gear engaged;
b) switching off the transmission system;
c) canceling initiation of start-up while the vehicle is still at rest; or
d) exceeding a predetermined speed which would normally be reached only under favorable driving conditions.
According to a preferred embodiment of the present invention, start-up from rest is initiated by movement of a drive-mode selector means from a xe2x80x9cneutralxe2x80x9d position to a xe2x80x9cdrivexe2x80x9d position.
Further control of wheel slip at low speeds may be achieved by the imposition of third gear after second gear has been imposed manually as start-up gear, if wheel slip is detected in second gear. Wheel slip may be detected by means of anti-lock braking sensors, slip being defined as a state where the speed of a driven wheel exceeds the speed of a non-driven wheel by more than a predetermined amount (typically 50 rpm) while the vehicle is moving at less than 5 km/h and the throttle is opened less than a threshold amount (typically 15%).
The imposition of third gear may alternatively take place if the driver uses the gear-selector lever to instruct an up-shift while wheel slip is detected during start-up from a standstill condition. Imposition of third gear may be canceled by:
a) switching off the transmission system; or
b) closing the throttle.
In accordance with a further embodiment of the invention, the driver may be required to take additional steps in order to avoid an unwanted increase of the start-up gear. For example, the driver may have to apply the main brake of the vehicle simultaneously with actuating the gear-selector lever.
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.